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United States Patent |
5,709,041
|
Tarplee
|
January 20, 1998
|
Device for recovering the heat removed by a load contained in a clothes
washing-drying machine or clothes dryer and for its reuse for further
drying said load
Abstract
A device for recovering heat during the drying of a load in a clothes dryer
of the once-through external air type, said machine comprising a tub for
containing a load to be dried, a conduit for feeding external fresh air
into said tub, and a conduit for expelling hot moist air from this latter
and for feeding it into the environment in which the machine is located. A
container is provided containing a phase change material or PCM in which
heat transfer surfaces or channels are present, along or within one of
these latter there passing at least part of the hot moist air from the
exit of the tub so as to transfer thermal energy to said PCM, which
changes its physical state or phase, within another of said channels or
along another of said surfaces there passing at least part of the fresh
air entering the machine and to which said energy is transferred by the
return of said PCM to its original physical state or phase.
Inventors:
|
Tarplee; Jennifer L. (Cedar Rapids, IA)
|
Assignee:
|
Whirlpool Corporation (Benton Harbor, MI)
|
Appl. No.:
|
742524 |
Filed:
|
November 1, 1996 |
Foreign Application Priority Data
| Nov 03, 1995[IT] | MI950758 U |
Current U.S. Class: |
34/595 |
Intern'l Class: |
F26B 011/02 |
Field of Search: |
34/86,595,596
|
References Cited
U.S. Patent Documents
4151398 | Apr., 1979 | Maake | 219/374.
|
4180919 | Jan., 1980 | Baltes | 34/449.
|
4908238 | Mar., 1990 | Vigo et al. | 427/389.
|
Primary Examiner: Sollecito; John M.
Assistant Examiner: Doster; Dinnatia
Attorney, Agent or Firm: Schwyn; Thomas A., Davis; Mark A., Rice; Robert O.
Claims
I claim:
1. A device for recovering heat during the drying of a load in a clothes
dryer of the once-through external air type, said clothes dryer comprising
a tub for containing a load to be dried, a conduit for feeding external
fresh air into said tub, a conduit for expelling hot moist air from the
tub and for feeding it into the environment in which the machine is
located, and means for heating the fresh air, the device comprising a
container containing a phase change material (PCM) in which a heat
transfer area is present, at least part of the hot moist air passing into
the heat transfer area from the exit of the tub so as to transfer thermal
energy to said PCM, which changes its physical state or phase, and at
least part of the fresh air entering the machine passing through the heat
transfer area and to which said energy is transferred by the return of
said PCM to its original physical state or phase.
2. A device as claimed in claim 1, wherein the PCM container is directly
connected to the fresh air inlet and is also directly connected to the
exit conduit from the tub in which hot air is present, the hot air stream
and the fresh air stream passing simultaneously through said container.
3. A device as claimed in claim 1, wherein the PCM container is connected
to the fresh air inlet via a first controlled valve member and a conduit,
said container being connected to the exit conduit from the tub and into
which hot air flows via a second controlled valve member and a further
conduit.
4. A device as claimed in claim 3, wherein the first and second valve
members are controlled by a controller which controls the operation of the
clothes dryer.
5. A device as claimed in claim 3, wherein the first valve member connected
to the fresh air inlet is connected to an inlet conduit to the heating
means via a conduit, the second valve member connected to the exit conduit
from the tub being connected to a further conduit bypassing the PCM
container and connected to the hot air exit.
6. A device as claimed in claim 1, wherein the heat transfer area comprises
heat transfer surfaces in the PCM with the portion of hot moist air and
fresh air passing along the heat transfer surfaces.
7. A device as claimed in claim 1, wherein the heat transfer area comprises
heat transfer channels in the PCM with the portion of hot moist air and
the fresh air passing through the heat transfer channels.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heat recovery device for a clothes washer-dryer
or dryer.
2. Description of the Related Art
In a clothes washing-drying machine or clothes dryer of the once-through
external air type, this external air is heated by usual heating means and
fed into the tub in which a usual rotary drum carries a load to be dried.
The air removes water from this load and becomes moist, said hot moist air
then being discharged to the outside of the machine.
With such a machine there is the problem of increasing temperature and
humidity of the environment surrounding the machine, with obvious problems
for the user.
Various arrangements are known for reducing the release of thermal energy
and moisture to said environment and at the same time achieving an energy
savings in the use of the machine by transferring part of this energy to
the air entering the machine, so as to heat this air and reduce the
temperature difference between the air entering the heating means and the
air leaving them. These known arrangements comprise air-air heat
exchangers of regeneration or heat tube type and heat pump systems.
Although these known arrangements achieve their purpose in a more or less
acceptable manner, they result in an increase in the volume of the machine
in which they are contained, with consequent problems related to the
greater space required for the machine. Such arrangements are also costly
and often complicated to mount in the clothes washing-drying machine or
clothes dryer, resulting in a higher final machine cost and difficult
maintenance.
In a clothes dryer or clothes washing-drying machine of condensation type,
for recovering the thermal energy of the hot moist air leaving the tub and
for transferring it to the fresh air entering this latter it is known to
use a device comprising a container containing a phase change material or
PCM.
These phase change materials (PCMs) possess two possible phases, namely a
solid phase and a liquid phase. Such materials (salts, acids, organic
materials, etc.) are generally solids and become liquid by the absorption
of thermal energy. On releasing this thermal energy they return to the
solid state.
Said known materials absorb or release heat or thermal energy by an
isothermal process caused by phase change, such as fusion and
solidification.
The known arrangement using PCMs in a clothes washing-drying machine of
condensation type cannot be used in a clothes washing-drying machine or
clothes dryer of the once-through external air type because of the
constructional differences in the once-through air circuit and because of
the need to heat the external air entering the machine, which is certainly
at a lower temperature than that of the circulation air entering the
heating means in a clothes washing-drying machine of the condensation
type.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a device for
recovering thermal energy within a clothes washing-drying machine of the
once-through external air type which enables the temperature difference
between the fresh air entering the heater and the air leaving it to be
considerably reduced, and which is compact, is simple to construct, and
uses a phase change material for this purpose.
This and further objects which will be apparent to the expert of the art
are attained by a device in accordance with the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more apparent from the accompanying drawing,
which is provided by way of non-limiting example and in which:
FIG. 1 is a schematic view of a first embodiment of a clothes
washing-drying machine provided with the device of the invention; and
FIG. 2 shows a clothes washing-drying machine similar to that of FIG. 1 but
provided with a second embodiment of the device according to the invention
.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to said figures, a clothes washing-drying machine or clothes
dryer (generally referred to as clothes dryer) comprises a tub 1
containing a rotary drum (not shown). It is connected by an inlet conduit
3 to a usual heating element, for example, of the electrical resistance
element type 4. This latter is connected by a conduit 5 to an inlet 6 for
fresh air originating from the environment external to the machine. A
conduit 7 carrying hot moist air leaves the tub. Usual circulation means,
not shown, circulate the air from the outside to the inside of the tub and
then back to the outside.
According to the invention, at least part of the fresh air entering the
machine and at least part of the hot moist air leaving the tub 1 are fed
to a container 8 containing a phase change material or PCM. To this
latter, the air leaving the tub transfers at least part of its contained
thermal energy (heat) removed from the load present in the tub, said
transfer resulting in a phase change of the PCM, which changes from solid
to liquid. This thermal energy is transferred to the entering fresh air by
the PCM returning to its initial phase (solid) to result in an increase in
the temperature of this fresh air. In this manner the temperature
difference between the air entering the heating element 4 and the air
leaving it is reduced. Consequently the energy required to heat this air
to the temperature necessary for drying the load in the tub is also
reduced.
Specifically, FIG. 1 shows an embodiment in which the energy transfer
between the hot air in the conduit 7, the PCM, and the entering fresh air
takes place simultaneously. In this figure the container 8 is traversed
simultaneously by a stream of hot air and a stream of fresh air. These
streams graze opposing surfaces of parallel and, for example, superposed
plates enclosing the PCM (not shown) and contained in the container 8. In
this manner the hot air present in the conduit 7 transfers heat to the
PCM. As a result of this the material tends to liquefy, but solidifies
very rapidly on transferring this heat to the fresh air entering. Compared
with a traditional heat exchanger there is the advantage that by suitably
choosing the PCM there is no danger of condensation in the heat exchanger.
Moreover, the energy accumulated can be preserved for the next drying
operation.
The container 8 (i.e., the superposed plates present within it) may contain
a single PCM or several PCMs of different phase change temperatures,
chosen according to the characteristics of the exit (hot) air and arranged
to optimize heat transfer from the hot air to the cold air (for example, a
first PCM changing phase at a temperature T1 and positioned along the hot
air path upstream of a second PCM with a liquefaction temperature T2 less
than T1). In the embodiment shown in FIG. 2, in the exit conduit 7 from
the tub 1 there is a valve member 12 controlled by the usual machine
function control member or timer (not shown). This valve member, of
three-way type, is connected to a first exit conduit 13 opening to the
outside of the machine, and to a second exit conduit 14 leading to the
container 8 and which, downstream of this latter, reconnects to the outlet
of the conduit 13. Likewise, in the conduit 5 there is a valve member 17,
controlled in the same manner as the valve member 12, which is connected
to the fresh air inlet 6 and to two exit conduits 18 and 19, the first 18
being an extension of the conduit 5 and the second 19 traversing the
container 8 and reconnecting downstream of this latter to the conduit 5.
In the embodiment shown in FIG. 2, the container 8 can contain either the
plates described with reference to FIG. 1 or a plurality of tubes through
which an air stream passes (for example the hot air stream) and which are
grazed externally by the other air stream (the fresh air stream), the PCM
being present in the wall of each tube.
In the embodiment under examination, energy recovery takes place in two
stages. During a first stage, the hot air leaving the tub 1 passes into
the container 8 before being expelled from the machine and transfers heat
to the PCM, which liquefies. In this stage the valve 12 connects the
conduit 7 to the conduit 14. In the second stage, the inlet air passes
through the container 8 before entering the heating element 4 and absorbs
heat from the PCM, which solidifies. This air is hence heated. In this
stage the valve 17 connects the inlet 6 to the conduit 19.
As an alternative, in the first of said stages it is also possible for the
inlet air to pass directly through the conduit 18 and the conduit 5. In
the second of said stages, the air from the conduit 7 can pass directly to
the exit via the conduit 13 without penetrating into the container 8.
The aforedescribed process can take place several times during one and the
same drying cycle or can take place during two successive drying cycles if
the second drying cycle occurs shortly after the first. In this case the
first of the aforesaid stages takes place at the end of the first cycle
and the energy recovery of the second stage takes place at the
commencement of the second drying cycle.
By means of the embodiment of FIG. 2, a drying process is achieved which is
more rapid and more efficient than that obtainable with the embodiment of
FIG. 1, although the device shown in this latter has the advantage of
greater simplicity and lower constructional cost than the embodiment of
FIG. 2. Moreover, in this latter an air circulation not involving the PCM
can be achieved, this being useful, for example, if the air through the
inlet 6 already has a high (ambient) temperature or at the commencement of
the drying cycle.
According to the invention, energy can be recovered within the container 8
(i.e., within the PCM) for a subsequent drying operation even some days
distant.
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